1. Field of the Invention
The present invention relates to a field of proximal cableless communication systems.
2. Background of the Invention
Two-way voice and digital communication links are well-known in the prior art. One class of these communicating devices involves cordless communication systems which are proximately disposed from each other. Typically, they include at least two transceivers permitting them to communicate full-duplex at transmission power levels which allow units to be separated 500 feet or so from each other.
Basic superhetrodyne techniques are used to receive an incoming signal, mixing it with a local oscillator generated frequency to provide an intermediate frequency (IF). Then the IF is detected and the resulting signal, such as audio, is amplified for end use. In transmission, the same transceiver unit accepts an input, such as voice, and modulates a carrier frequency. The resulting modulation envelope is amplified in a power amplifier for transmission. When only short-range communication is desired, the transmission power levels are reduced in the above-described technique.
It is appreciated that transmission of signals between two short-range transceivers, such as in cordless telephone units or "walkie-talkies", still entail the necessity of communicating across an appreciable distance. To provide signal transfer across this distance, a nominal power level, albeit low, is still required for transmission of intelligence. Such transmission will require a similar circuit as described above. When communication at a much shorter distance is required, prior art practice has resorted to signal transfer over lines or cables. One such example is the use of a headset by connecting a headset to a base unit by cables. Such direct physical connections are used because of simplicity and cost savings. However, such physical connections significantly restrict the mobility of the user.
As described, the present invention permits full duplex two way communication within a limited range without the need for complicated circuitry to provide the transmission of signals. Further, the present invention permits significant increase in user mobility. At the same time, the limited range of the apparatus of the present invention results in improved security and isolation from interference due to the proximal range of the devices.